Claw pulldown mechanism



JASPER S. CHINDLER INVENTOR 1;? P Q ..;@.2M 3/ 2 j ATTORNEYX Sept. 23,1952 J. s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 3 Sheets-Sheet 1 P 1952 J.s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 v 3 Sheets-Sheet 2 JASPER S.CHANDLER INVENTOR P 1952 J. s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 5 Sheets-Sheet 3 (1, ANGLE0F CAMSHAFT ROTATION, DEG/FEES JASPER S. CHANDLER 2 7 kNVENTOR BY z Z WATTORNEi Patented Sept. 23, 1952 CLAW PULLDOWN MECHANISM Jasper S.Chandler, Rochester, N. Y., assignor to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey Application February 24,1950, Serial No. 146,110

11 Claims.

1 The present invention relates to improvements in claw-typeintermittent film-advancing mechanisms for handling perforatedmotion-picture Although many types of intermittent film-adyancingmechanisms for motion-picture cameras,

projectors, perforators, printers, etc., have been designed, these knownmechanisms possess certain disadvantages in spite of the great amount ofeffort and development work which has been devoted to this problem.

The primary object of the present invention is the provision of anintermittent film transport mechanism of the claw-type which possessesthe following advantages strived for in the art: The mass and dimensionsof the moving parts are substantially reduced to the end that high-speedoperation is possible with reduced forces of acceleration, reducedrubbing velocity and, hence, reduced wear on the parts; the follower isnormally held in contact with the driving cam by a spring which not onlyprovides the force for effecting the return and film-engaging motions tothe claw, but providesautomatic take-up in the event of wear on the camand cam follower surfaces, thus providing accurate positioning of thefilm and reduced noise of operation over a long period of time; thespring is tuned to cancel out the fundamental harmonic, and actuallycertain portions of the higher harmonics of the claw accelerationalforces, to thereby reduce the working pressure between the cam andfollower surfaces; the cam has a configuration primarily useful forapparatus other than projectors, although it could be modified for usethereon; the cam provides a pull-down angle of approximately 130characterized by the fact that approximately one-half of this pull-downangle produces positive acceleration and the remainder produces negativeacceleration with a gradual tapering off at the end position where theclaw comes to a stop before being withdrawn from'the film path and, as aresult of which, the advance of the film is smoothly and accuratelystopped at the desired end position; the top and bottom edges of theclaw tip are tapered inwardly to a slight degree and the cam is sodesigned that the claw completely fills the perforation when moved intoengagement therewith, whereby the claw has control of the film bothduring the positive and negative accelerating movements thereof, andthere is no sawing action between the bottom claw edge and the bottomedge of the engaged perforation; an auxiliary cam and follower areprovided which preventsthe cam follower from accidentally leaving thedriving cam due to. any unusual occurrence during the engagement of theclaw with the film, and which auxiliary cam takes over, in combinationwith the driving cam and its followers, to permit reverse operation ofthe claw mechanism for feeding the film in the opposite direction; andguiding means are provided on said driving cam or auxiliary cam followerwhich cooperate with their companion parts to guide the claw laterallyin a given plane of movement; and the contour of the driving cam is sodesigned as to eliminate any sudden changes in the acceleration of thecam-driven parts during the operation cycle.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its methods ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

Fig. 1 is a schematic showing of a pull-down mechanism constructed inaccordance with one embodiment of the present invention and shown inassociation with a film gate and film path of any type of apparatusadapted to handle motionpicture film;

Fig. 2 is an enlarged elevational view of the pull-down mechanismshowing the position the parts assume when the claw is at the top of thepull down stroke;

Fig. 3 is a view corresponding to Fig. 2 but showing the claw at thebottom of its pull-down stroke; V

Fig. 4. is an enlarged view of the tip-0f the claw showing theconfiguration thereof and the position it assumes relative tothe engagedfilm perforation'when at thetop of the pull-down stroke, or in theposition shown in Fig. 2;

Fig. 5 is similar to Fig. 4, but showing the tip of the claw in theposition it assumes relative to the engaged filmperforation when theclaw is at the bottom of its pull-down stroke, or the mechanism is inthe position shown in Fig. 3;

Fig. 6 is a diagrammatic illustration of the path described by the tipof the pull-down claw during operation of the mechanism;

Fig. 7 is a sectional view taken substantially on line ll of Fig. 2 andshowing how the fianges on the driving cam guide the claw memberlaterally; I

Figs. 8, 8-a and 8-22 diagrammatically illustrate how the parts of thefollower mechanism enter into the design of the spring in order to tunethe spring so as to cancel out the fundamental harmonic; H I

Fig. 9 is an enlarged elevational view showing another embodiment of thepresent invention, particularly designed to permit feeding of the filmin the reverse direction, as well as to prevent accidental separation ofthe follower surfaces from the driving cam;

Fig. 10 is a sectional view taken substantially on line l0|0 of Fig.9;

Fig. 11 is a diagrammatic view of the cam and Like reference charactersrefer to corresponding parts throughout the drawing.

Referring to Fig. 1, basically this pull-down mechanism operates in thesame manner as conventional claw pull-down mechanisms-'inthat thefilm-at the gate. This shaft may be rotated at a constant desired speedby any suitable mechanism including a driving wheel 14 coaxial therewithand located to one side of the film path;

Engaging the periphery of the driving cam 12 is a follower in the formof a Y, which is pivoted on a pin I 5 carried on the end of an arm 11and which arm is, in turn, pivoted on a fixed pin 18 whose axis isparallel to that of the cam shaft 13. A coiled spring S wrapped aroundpivot pin 18 has one end [9 engaging arm I! and normally acting to moveit and the follower in a clockwise direction, or toward the cam. Theinside edges of the two branch arms 20 and 2| of the Y-shaped followerengage the periphery of the cam and constitute follower surfaces 22 and23 which, as indicated, may be separate hard-wearing inserts, i. e.,sapphire, carboloy,- etc. On the end of-arm 2| is formed thefilm-engagingclaw 24-.

As will be apparent from an inspection of Figs. 2 and 3, the peripheryof the driving cam I2 is completely irregularwith respect to its axis ofrotation. In advancing the film, the cam rotates counterclockwise andthe cam and follower are so designedthat both follower surfaces 22 and23 are in simultaneous engagement with spaced points on the camsurface-atall times. The cam is so formed that it, in combination withthe pring S, causes the claw tip to describe a path of the type shown inFig- 6. The cam positively drives the claw downwardly: and out ofengagement with the film perforation at the end of the pull-down stroke,while the spring S provides the power to return the claw to the top ofits stroke and then back into engagement with the successive filmperforation. The opposite sides of the cam extend slightly beyond theperiphery of the cam surface to constitute guide flanges 25 whichoverhang opposite edges of the follower surfaces 22 and 23, and thusserve to laterally guide the follower and claw in their given plane ofmovement. This guiding action of flanges 25 is most clearly apparentfrom an inspection of Fig. 7.

This cam i2 is so designed that the pull-down stroke takes approximately130 of the cam rotation as distinguished from 60 to 72 pull-down anglesnormally used in the cams of claw mechanisms of this type. While thispull-down angle is not suitable for use on motion-picture projectors,wherein quick pull-down times are required, it is suitable for all othertypes of motionpicture apparatus including perforators, printers,cameras, etc. The advantage" of this large pulldown angle is that theaccelerational forces re- '4 quired to move the film can be reduced toonefourth of those requiredfor a-65.pull -down angle due to the factthat more cam movement is available to get the film up to speed, and tostop it, and this relationship varies inversely as the square of thepull-down angle. It will be ap- --parent-that -this cam shape could beredesigned ,-to..gi ve a-smaller pull-down angle and thus be adaptedfojruse on projectors, but then certain advantagesof the-same (so far as lowaccelerational forces are concerned) would be lost. Also, a skip strokearrangement without alteration of the cam could be used for projectoroperation.

01' this pull-down angle, approximately half thereof is usedtoaccelerate the claw. The remainder of'the-pull-down'angle is used todecelerate the clawsothat it will come' to a stop gradually at the'endofits stroke and only very low inertia forces of the claw, or film,will be present and tend to carry the film past -a given bottomposition. The last 4 or -5 degrees of the pull-down movement take placeat a very much reduced value of deceleration prior to withdrawal of theclaw from the" engagedperforatidn; This insures the film beingcompletely 'stoppedand accurately located at the'time'the claw leavesthe engaged perforation. Thecam' surface is so designed that thecharacteristic curveot the'acceleration forces during the entiremotionhas no sharp. corners, as is characteristicfiof the Lumiere,constant acc'elerationand other' type cams; but the changesinnc'oelerational forces, bothin direction and magnitude, are'smo'othedout. This results in. less wear in the cam and follower surfaces duetoaccelerational-forces and appreciably reduces noise. ofroperation. Thisis done by the technique of Fourier analysis .and the eliminationof-all-harmonics above the 10th.

With this cam and follower constructiomthe parts can be reduced-in sizeand-mass-as compared with conventional claw mechanisms for doing thesame job; Forexample,I have found that, a cam approximately long in thelong dimension :and long onthe short dimension, will give theadvance'stroke' required when using a 16 mm. movie filmr Reductionin'overall dimensions of the cam results in reducing the rubbingvelocity, and, hence, we'ambetween the cam and follower surfaceswhilereduction in m'ass makes possible-higheroperating speed'sL--- I havefound that a claw mechanism of this type can be operated at speeds atleast as high 1 as 1950 R; P. M. for long-periods of timewithoutdifficulty. An examination of thecam' and follower arrangement will showthat actually thecam and follower surfaceshave only a two-point'contactat any one position of the mechanism.

As clearly indicated in Figs. 4 and 5, the tip of the .film claw Z'l'hasits top and bottom edges 28 and 21 respectively inclined toward oneanother result of which, no impact between'the edges-of th perforationand edges 'of thef claw-are encountered at any time. Smallamounts ofpitch variation in the film 'are accommodated before the-start of theadva'nce'stroke. I have'fo'und that the edges26 and of 'th'eclaw areinclined 4 inwardly relative to the remainder of the 'correspondingportions of the claw, very satisfactory results are obtained.

The cam and follower are so designed that at the top of the stroke thetop edge 26 of the claw is horizontal and parallel ,to the top edge ofthe perforation. See Fig. 4. This means that the bottom edge 21 of theclaw lies at anangle of 8 relative to the bottom edge of theperforation. At the bottom of the pull-down stroke, these conditions arereversed; namely, the bottom edge 21 of the claw is horizontal andparallel to the bottom edge of theperforation, and the top edge 26 makesan 8 angle with the top edge of the perforation. See Fig. 5. Thiscondition makes for accurate positioning of the film in either forwardor reverse direction of operation, even if the claw tip has not enteredto the full depth. This rocking motion of the claw tip through 8 duringthe pull-down stroke does not introduce a sawing action between thebottom edge '21 of the claw and the bottom edge of the perforation,because the cam and follower mechanism are so designed that, during theslight rocking motion of the claw, the dimension X, shown in Figs. 4 and5, remains constant throughout the pull-down stroke of the claw. Thisindicates that the same point on the edge 21 of the claw which engagesthe bottom edge of the perforation of the claw at the top of the strokealso engages the perforation at the same point at the bottom of thestroke.

Coming now to the primary novel feature of my pull-down mechanism whichdistinguishes it from the prior art more than any other mentioned up tothis point, I have found that certain definite advantages can beobtained by tuning the spring S to the operating speed of the pull-downmechanism, whatever it might .be. This tuningof the spring S cancels outthe fundamental harmonic, and actually certain amounts of the higherharmonics, in themechanism. The result of this is that the springactually takes care of part of the accelerations and dec'elerations ofthe springmoved mass when operated at the specified speed with theresult that the remaining forces between the cam and follower surfacesare appreciably re: duced, along with a corresponding reduction in wearon the cam and follower surfaces. In fact, I have found that by tuningthe spring, the forces between the cam and follower as compared to thosefor a low rate spring are reduced by 30 to -75 per cent, depending uponthe portions of the claw stroke being considered. For instance, theforces between the cam and follower surfaces are reduced 30 per cent atthe peaks in the pull-down stroke and in the return stroke; the peakforces occur at the points where the downward accelerational forces,plus the upward spring forces, are at a maximum. This reduction inaccelerational forces becomes significant when it is noted that theacceleration may amount to as much as 42 gs at the film for an operatingspeed of'l950 R. P. M.,see Fig. 12. v

The tuning of this spring involves calculating the spring constant, orspring stiffness, required to vibrate the movable follower mechanism atthe frequency the device is to operate and then from this constanttocompute the size of spring having this desired constant. The calculationof the spring constant involves solving the following formula:

in which fr is the operating frequency in cycles per second to which thespring is to be tuned; K is the spring constant referred to'agivenconvenient point in the moving system; and M is the equivalent mass ofthemoving parts acted on by the spring including follower l5, arm [1,and pivot pin le (the mass is equal to the. weight divided by g, thestandard acceleration of gravity or 386 in./sec. referred to the sameconvenient point in the moving system. After the value K" is determined,the spring can be computed from the following formula forra. cylindricalhelical spring of circular cross-section, if that is the type used, asin the present instance.

where f is the deflection and P is the force, both referred to theradius r,

l is the wire length,

E is Youngs modulus, and

d is the wire diameter of scale for purposes of clarity, the first stepis to find the. equivalent mass of each part or the follower mechanismwith reference to a given point in the moving system.

The weight of the claw member part shown in Fig. 8 and being s thick wasfound to be 1.574 gr.=.00347 lb. The natural frequency of the claw partwasjthen found to be 140 C. P. M. by suspending it as a pendulum at aradius of 2.145 from the normal film plane. This center of suspensionindicatedat A in Fig. ;8 was found by the intersectionof vlinesdrawn at4*, to the'film plane at the top and bottom of the claw stroke which is.300" in a single frame of 16 mm. film. This point of suspension waschosen because it represents the equivalent center about which the clawtip must rotate so that the same will enter the film perforation withits inclined upper edge perpendicular to'the film plane and leave thefilm perforationat the bottom of the stroke with its lower. edgeperpendicular to the film plane. The weight of arm H was found to be1.97 gr.= .00434 lb. and its natural frequency when suspended at theright-hand edgeof the 3%" hole was found to be 212 C. P. M. The locationof the center of gravity and its distance from the point of suspensionwas next determined for both the claw and the arm.

is The radius of gyration"lc was then found for both the arm andclawmember from the formu a:

mzw

per minute, and 0 1s the distance of the'center of gravity from thesuspension point Weight of pivot pin-16 connecting arm"z'whichsiszderived iromithe .formulaeior-aygravity orphysical'pendulumand-is For 'arm' where i=radius of gyrationneferred'tocenter of gravity at :center of hole to claw member:.=.000328'lb.

Equivalent weight oi clawmember: at (l;741 zmdosgs 1b.

left-end of arm 17 1 .625

. Equivalent weight of arm at lcitaend ct it 001535 1b V 1 K=..63l1114.111. 7 T To compute a spring havingi-the-Rduird .con-' I stant, itis -necessary toassumea 'giverr diameter --ofspring andsubstitute: in:the iollowmgcior- -mula:

If we zallowthecspringi to have 5.coi1s;then the mean coil diameter andoutside diameter: .488

It. is also necessary to calculateithe maximum spring stress todetermine if this is a safe value. We use the formula,

. -IardJS, a?

where 85 is tensile and compressive stress The value P must1be-determined first. Total travel at arm end= :where r'r' is the'period-mi thewpezidulumimsec- I onds For, claw member .=Allowing abouteiadditionai motion .for initial loading of spring l1 MaxP=-(.'238+:L094).;631

. '.2Q911b. Substituting "this valuenof Pain ,theiorm'ula 1 andsolvingliorss Accordingly; f or tuningjthe-spring in question, f-thespring shouldihave'- 5 turns; an outside coil diameter. equal:to:..488f'; a #wire diameter equal *t0fi0390 hand about initialspringdeflection measurediat arm end.

The contours ofconventionalcams usedin film pul'ldown' mechanisms -have"characteristic accoloration curves; having: sharp corners and sud-;den'changesoflarge-magnitude as evidenced by verticallines "in thesolid line curve of Fig. 12. Theselsharpcurves are :the result of high"harmonics .being present in the Fourier, analysis of "theoperationcycle. I--have discovered that if "the contour ofthe'camis'modified tosmooth out "the sharp corners and eliminate sudden changes"in-'accelerational forces '-without changing the path of movement ofthe-clawfrom that desired, that anappreciableamount of noise and'wearbetween-the cam, and "follower; surfaces can be eliminated.

In the following table I show the "comparison "oi-the camcontoursfor aconventional cam designed to "give the desired path ofjclaw travel-shown'inFig. 6 and one having a contourmod- :ified 1 according to'fthe' present ,invention to smooth-out the acceleration curve.

' Table 345 a B (modifled) .3351. 111. :19 111.40 0 1 112.45 112.186 911s. 15 118149 .118 :1 130.86 .1130. so 21 148. .149. 01 7 -60 36 112.49112.72 names 199.- 14 .64 .225.11 225.68 7 63 149.13 249; 81 I 12 11,0;26 210. ,1 81 287.74 287.70 -90 301. 44 301. 56 99 311.02 311.11 108316. 25 315, 13 111 1 316.48 316.22

v :;In this .table: 6o wfi=Cam rotation angle relativexto follower,- in

I ,-degrees B=Perpendicular distance from'camaxis of'ronation .to ..leftlffaceoi scam followerv surface, in ,mils.

. .See .Fig l-lrnln this table only. thezadvance portion oflthemotion-is shown, .but .the modifioationlwill extend in similar fashion.throughoutjthe. 3602M. rotation. Theacceleration curves.,iorcthesetwoflcams areshown in- Fig. 12.

'The unmodified cam contour is characterized by portions having aparabolic relationship between ;8 and B and portions of circular arcs sochosen as to provide the required him advance in the specified angle ofrotation, and the rewrmaining portionsof.1c1aw travel; due considerilycalculated.

ation being given to the fact that both followers ride on the same camand to the arrangement which gives a minimum cam size. The modifiedcontour is found by taking as few terms as necessary of the Fourierseries for the unmodified case (10 termsfor this example) in order toprovide the desired claw motion without undue rounding of the corners ordeparture from the straight portion of the claw path shown in Fig. 6.

Cams with straight followers employing the parabolic relationshipbetween 18 and B (also called constant acceleration cams since theseoond derivative of B with respect to 18 is a constant) and cams madeup partly, or entirely, of circular arc segments of finite valuesatdifferent radii and center locations (usually called Lumiere cams) arewell known. The most common cams. are usually symmetrical in shape,

and quite often are of constant diameter so that,

they will work between parallel straight followers. Such cams need notbe symmetrical, however, as in the unmodified profile of the examplegiven in the above table.

Both the .constant acceleration cams and the Lumiere cams havethe'advantage of being eas- Constant acceleration cams produce a givenmotion with the minimum possible peak value oft-he second derivative ofB with respect to c (for rectilinear motion of the follower, this alsomeans minimum acceleration for constant drive shaft speed). oweconsiderable of their popularity to the fact that in the absence of camgenerating and re producing equipment they offer some simplicity oflayout and construction.

Referring to Fig. 12, it will be seen that in the acceleration curve forthe unmodified cam, the first or negative acceleration portioncorresponds to a portion of the cam following the parabolic relation,and that the second or positive acceleration portion corresponds to aportion of the cam consisting of a circular arc. .In both cases thereare sharp corners andsudden changes of large magnitude. Since the forcesbetween the claw tip and the film, and between the cam and its follower,are both directly related to the acceleration, it follows that shockloadings would exist in the unmodified case. The sudden force changesare productive of vibrational noise and wear. The situation is analogousto the sudden application of full throttle or full braking force on anymoving vehicle. The sharp corners and the vertical lines of theunmodified acceleration curve are l the result of high harmonics beingpresent in the Fourier analysis of the operation cycle.

The modified curve results from the elimination of all of the harmonicsabove the 10th. The change in the acceleration curve is very pronouncedwhile the actual change in the cam shape and claw path, althoughimportant, is small, see table above. Another mannerof distinguishing acam modified according to this invention from a constant accelerationcam or a Lumiere cam is that in my modified cam no finite length of thecam sur'faceis arcuate in shape, and each curved portion of the camsurface blends into the adjacent curved portions so that there are nosuddenchanges. in curvature, and hence acceleration, caused by .afollower passing from one portion to the next. As mentioned above, aLumiere camflis characterized by being made up either partly or entirelyof circular arc segments offinite. length,

Lumiere cams whereas constant acceleration cams, although their surfacedoes not include arcuate portions, are characterized by sudden changesin curvature and acceleration between successive parabolic portions. I

In addition to the reduction of noise-and wear, the modifiedacceleration curve provides the significant advantage of gradualreduction of the force near the end of the advance stroke. This reducesthe tendency of the film to over-shoot or travel past the correctstopping position, for a given frictional retarding force applied to thefilm, probably. at the gate. The accuracy of film location is therebyimproved, and in some types of apparatus this of considerable importance(i. e;, to produce steady pictures in oin-camerasor in step-printers),and. it is anticipated thatan even more pronounced reduction in theacceleration force near the end of the advance stroke may be desirable.It will be appreciated that in the curves of Fig. 12 only that portionof the claw travel constituting the actual pull-down stroke of the clawhas been shown. This includes approximately 130 (from 350-120) and isindicated on Fig-6.

, Referring now to Figs. 9 and l0, a modification of the claw pull-downmechanism already described whichpermits feeding of thefilm in theopposite direction for any reason will now be described. As before, thismodified mechanism comprises a Y-shaped follower l5 pivoted to the endof arm IT by a pivot pin l5; said arm, in turn, being pivoted at itsother end to a fixed pivot E8. The follower surfaces 22 and 23' on thefollower I5 are normally pressed into engagement with a driving cam 12by a coiled spring S, the driving cam having the same contour as in thefirst embodiment and aloneserving to drive the film in a forwarddirection and withdraw'the claw from the film path, while in combinationwith spring S controlling the-return travel .of the claw and its returnstroke into the film path. Also as before, the follower includes a claw24' adapted to engage the film perforations for driving purposes. I havealso shown it as including a second claw 39 which is spaced from claw24' by a distance equal to theframe or perforation spacing of the filmand engages the perforation immediately following the; one engaged bythe feeding claw. This second claw 30 is provided to take over thefeeding of thefilm in the event the claw 24' misses its intendedperforation engagement for any reason, such as, ir-

regular perforation spacing due to film splices,

mutilated perforations, etc. Normally, the second claw 30 does no Workwhatever. Up to this point, this modification of the pull-down'mechanismis the same as that first disclosed,both in structure and principle ofoperation. r

In order to. permit reverse film-feeding operation a second cam wasadded to the cam shaft to work in conjunction with cam 12', the two camsbeing then boxed in by an addition to the follower [5' which includes athird follower surface for engaging the second cam. To this end, I haveshown the second cam referred to as being two like peripheral cams 3! ofthe form best shown in Fig. 9 and mounted in alignment with one anotheron opposite sides of driving cam l2 and having the same axis of rotationas cam, l2.

Branch arms of follower 15 are then joinedby arcuate portion 32 lying insame plane as cam l2 and supporting arcuate follower surfaces 33disposed to engage the peripheral cams 3|. The .arcuate followersurfaces 33 are each provided with -aflange 34--whiehyoverhang theperiphery of its-corresponding-camiiand cooperates with a machined orfacedborder-35 thereon to laterally guide-the claw and follower duringoperation. See Fig. 10. These flanges serve the samef-unctionasfiangeslion cam I2 in-the-first-embodiment ofthe mechanism disclosed.See Fig. 7.

It is pointed out-that in thenormalforward feeding ofthe film, cams 3l-and'followersurfaces 33 are ca1led-uponto -do' nothing. Accordingly,

these-parts are so designed that when thedevice isoperating inaforWard-direction'there isa slight clearance; i. e., .001 or.002'in.between -follower surfaces 33 andcams 3l,"as indicatedat"36'inFig. l0. By virtue of this clearancathere is-no wear between-cams3| and follower-surfaces 33 when the pull-down mechanism is operating inits forward direction and under normal-conditions.

However,--when it is I desired to -feed-thefilm in the reversedirection; the direction of rotation of thecam shaft I 3-is reversed andcams'3l and "follower surfaces -33 come into-engagement -to positivelydrive the claw into-engagement with the film at the bottom of the strokeand upwardly during the' time'the claw is in engagement with thefilm-perforation. It will be appreciated that in thismovement'the-forces between the cams-3| and their follower surf aces I33 are reduced by the normal action of sprin --S, which constantly tendsto move, the claw arm in'thesctwo directions. Withdrawal -of-the claw'from the "film path at the top of the stroke and downward movernentthereof'is then-takenover by cam' 12' engaging follower surfaces 22' and=23-on' the claw member, followers 33 being removed from require moreforce than the springpressurealone to hold follower surfaces 2-2 and 23''in engage- -ment with cam l2.

Cams 3! are-so designed that, in reverse operation'of the mechanism, theclaw tipwill-follow exactly the same path that it-does-in 'forwardoperation; namely, that shown in Fig. '6. Such a cam configuration-isreadily obtained without calculation by deciding where-thefdllowersurfaces 33 should be and operating. a claw arm of the typeshownin Fig.9 in the forward direction-by only the cam -l2 but with a blank of metalfixed to the -face'-thereof in overhanging relation with one -of thefollowers 33. As the claw mechanism is operated intermittently, thepoints at which the follower '33 passes over the metal blank can bescribed thereon, and'thenthe scribed'blank can be cut toshape on amilling-machine. -By such a procedure, a large scale master can be madein conjunction with the master already made for cam l2. From such amaster cam any number duplicates can be reproduced readily and accurately on a pantograph profile milling machine, as is well known.Asindicated in Fig. .10, both cams 3|, as well as cam I2, along with thecam shaft 13', are preferably cut from a :12 single piece "of stock soas to eliminate the problem of; properly orienting the several parts.

"The hole -i-I shown in-each of the cams 3| and-l2 in'-Figs. 9 and 10 isfor the purpose of reducing-the mass'of these parts.

while-'cams 3l-"appear to be regular in shape, actually they arecompletely irregular relative to the- 'cam' shaft'axisas is the drivingcam l2.

"Ofihand, it might be confusing that cams -3I differ in shape from cams[2, although the claw -tip traversesthesame-pathin both directions of"film feed. This is required, however, by the location and shape of thefollowers 33 as compared to the followers 22 and 23'. It will be obviousthatlt-he two cams "3| and the two fol- *lowers 33 could-be" replaced bya single cam and follower placed on either side of the oam [2' and its"followers- 22'and 23 and still obtain :specific :emhodiments :of :myinvention, I am xfullyaware .thatmanymodification's thereof arepossible. invention, :therefore, is not to be limited to :the.:precisedetails of construction shown and' zdescribed, .but .is intended tocover ;all:modificationszcoming:within the scope of the appended claims.

,1 .Having. thus described .my invention, what I zclaimasirnewrand-desire .to secure by letters Patent of .the United States is:

1-1. .A .cameoperated gpull-down mechanism for intermittentlyadvancing-a perforated film along a rgivenrpath-rand comprising arotatable pezripheral cam-whose axis .of rotation extends substantially;parallel to, and laterally of, the @film .path, a :cam follower havingtwo follower surfaces disposed in acute angular relation to onexan'otherandradapted to engage said cam, :a :claw'on' said-follower for engagingand adyancing-thefllm once for each revolution of "saidzcamrmeans formounting said cam follower -so that .it is free to move relative to the.filmgpath zunder :control -.of said cam in directionsto move the clawthereon longitudinally and -;perpendicularlyof said film path, means forrotatingsaid cam .at aespeed .to oscillate said claw ata frequency of m.strokes per minute, and means. including a spring normally urging saidifollowerein a-direction to hold the two followersurfaces thereof .incontact with said cam, -.-said .-follower and .spring.-urging meanshaving anatural freguemzyequal to n oscillations per minute whereby .theworking pressure between -sazid cam [and follower surfaces, .and hencewear on said two parts, is reduced.

v2. Aram-operated pull-down mechanism in accordance with claim. .1, andcharacterized by :the fact that'zsaid team has .a contour no finiteportion of. which-is arcuate with respect to a singlewcenteraand allvadjacent curve portions thereof blendin'to each other without a suddenchan'gexin'. curvature, whereby the acceleration curve thereofi's devoidrofsharp corners and sudden:;changes :of elargexmagnitude.

35A icam operated ipull-down mechanism for intermittently advancing aperforated film along a given path and comprising a rotatable peripheralcam whose axis of rotation extends substantially parallel to,andlaterally of, said film path, a cam follower having two followersurfaces disposed in acute angular relation to one another and adaptedto engage said cam, a claw on said follower for engaging and advancingthe film once for each revolution of said cam, means for mounting saidfollower so that it is free to move under control of said camto movesaid claw through a closed path to ad vance the film and has itsfollower surfaces nor: mally held in contact with said cam'and includingan arm pivoted at one end on an axis parallel to the cam axis, anextension on said follower pivoted to the other end of said'arm, aspring acting on said arm, means for rotating said cam at a speed tooscillate said claw at a frequency of n strokes per minute, said arm,spring and follower combination having a natural frequency of noscillations per minute, whereby the spring and parts moved thereby aretuned to cancel out the fundamental harmonics and certain portions ofthe higher harmonics and thereby reduce the working pressure between thecam and follower surfaces.

4. A cam-operated pull-down mechanism; according to claim 3,characterized by the fact that said cam includes flanges extending fromopposite sides beyond the entire peripheral face thereof, said flangesarranged to engage opposite edges of said follower faces to laterallyguide said follower in a given plane of movement.

5. A cam-operated pull-down mechanism according to claim 3,characterized by the fact that said cam has a configuration to impart tothe claw a pull-down stroke consuming approximately 130 of rotation ofthe cam and characterized by a positive acceleration, throughapproximately one-half of said Pull-down stroke followed by negativeacceleration through the remainder of the stroke until substantially theend of the stroke where the negative acceleration is gradually reducedto zero at the end of the pull-down stroke.

6. A cam-operated pull-down mechanism according to claim 3,characterized by the fact that the top and bottom edges of the claw areinclined toward one another by substantially 4 from the horizontal, andthe cam configuration being such as to cause the claw to enter the filmperforation at the top of the stroke with the top edge of the clawsubstantially horizontal and parallel to the top edge of the engagedperforation and to a depth such that the claw fills said perforation andleaves the perforation at the bottom of the stroke with the bottom edgeof the claw substantially horizontal and parallel to the lower orengaged edge of the perforation.

'7. A cam-operated pull-down mechanism for intermittently advancing aperforated film along a given path and comprising a rotatable shaftwhose axis lies substantially in a plane parallel to that of said filmpath, a first peripheral cam on said shaft for feeding the filmforwardly when the shaft is rotated in the direction of forward movementof the film, a cam follower including a claw thereon for engaging andadvancing said film, two follower surfaces on said follower disposed inand adapted to simultaneously engage two spaced points on said cam inall positions of said cam, means for mounting said follower so that itis capable of movement under control of said cam in directions to movethe claw thereon longitudinally and perpendicularly of said film path asnecessary to intermittent movement of the film thereby, a springnormally urging said follower toward said cam to maintain-both of saidfollower surfaces in contact, therewith at all times, and means forpositively preventing said cam follower from jumping off said cam forany reason and for intermittently feeding the film in the oppositedirection upon rotation of said cam shaft in the opposite direction. 7

8 A cam-operated pull-down mechanism for intermittently advancing aperforated film along a given path and comprising a rotatable shaftwhose axis lies substantially in a plane parallel to that of said filmpath, a first peripheral cam on said shaft for feeding the filmforwardly when the shaft is rotated in the direction of forward movementof the film, a cam follower including a claw thereon for engaging andadvancing said film, two follower surfaces on said follower disposed inand adapted to simultaneously engage two spaced points on said cam inall positions of said cam, means for mounting said follower so that itis capable of movement under control of said'cam in directions to movethe claw thereon longitudinally and perpe'ndicularlyof said film path asnecessary to'intermittent movement of the film thereby, a springnormally urging said follower toward said cam to maintain both of saidfollower surfaces in contact therewith at alltimes, and means forpositively preventing said cam follower from jumping off said cam forany reason and for intermittently feeding the film in the oppositedirection upon rotation of said cam shaft in the opposite direction, andincluding a, second peripheral cam mounted on said shaft in side-by-siderelation with said first cam, a third follower surface fixed to said camfollower substantially opposite the vertex of the angle formed by saidfirst two follower surfaces and in a position to engage said second cam,said third follower surface and second cam relatively disposed to befree from engagement when the first cam and two follower surfaces areoperating normally to advance the film in a forward direction andadapted to come into engagement only when said two follower surfacestend to leave said first cam for any reason and when the shaft isrotated in a direction opposite to that in which it is rotated toadvance the film.

9. A cam-operated pull-down mechanism for intermittently advancing aperforated film along a given path and comprising a rotatable shaftwhose axis lies substantially in a plane parallel to that of said filmpath, a first peripheral cam on said shaft for feeding the filmforwardly when the shaft is rotated in the direction of forward movementof the film, a cam follower including a claw thereon for engaging andadvancing said film, two follower surfaces on said follower disposed inand adapted to simultaneously engage two spaced points on said cam inall positions of said cam, means for mounting said follower so that itis capable of movement under control of said cam in directions to movethe claw thereon longitudinally and perpendicularly of said film path asnecessary to intermittent movement of the film thereby, a springnormally urging said follower toward said cam tomaintain both of saidfollower surfaces in contact therewith at all times, and means forpositively preventing said cam follower from jumping off said cam forany reason and for intermittently feeding the film in the oppositedirection upon rotation of said cam shaft in the opposite direction, andincluding a second peripheral cam mounted on said shaft in side-by-siderelation with said first cam, a third follower surface fixed to said 0amfollower substantially Oppositethe vertex of the angleformedbysaidfirsttwo follower surfaces and in a position to engage saidsecond cam, said third follower surface and second cam relatively dis-'posed to be free from engagement when the first cam and two'followersurfaces are operating normally to advance the film in a. forwarddirection and adapted to come into engagement only when said twofollower surfaces'tend to leave said first cam for any reason andwhenthe shaft is rotated in a direction opposite to that in which it isrotated to advance the film,- and flanges extending from opposite sidesof said third follower into overhanging relation with opposite sides ofsaid second ca'm to laterally guide said two fol lowers to movement in agiven plane.

10. A' cam-operated p'ulldown mechanism for intermittently advancing aperforated film along a, given path, and comprising a rotatableperipheral cam whose axis of rotation extends substantially parallel to,and laterally of, the film path; a claw arm having a, follower surfacenormally engaging said cam; a claw on said arm foren gaging andadvancing the film; means for mounting said claw am so that it is freeto move rela tive to the film path under control of said cam indirections to move the claw longitudinally and perpendicularlyof saidfilm path; said cam having a contour no flnite portion of which isarcuate with respect to a single center and all adjacent curve portionsof which blend into'each other without a sudden change in curvaturewhereby the acceleration curve thereof is devoid of sharp corners andsudden changes of large magnitude.

11. A; cam-operatecl'pull-down mechanism for intermittently advancing aperforated film along a given pathand comprising a rotatable peripheralcam whose axis of rotation extends substantially parallelto,- andlaterally of, the film path; a claw arm having a follower surfacenormally engaging said cam; a claw on said arm for engaging andadvancing the film; means for mounting said claw arm so that it is freeto move relative to the filin path under control of said cam indirections to move the claw longitudinally and perpendicularly-of saidfilm path; said cam having a contounwhich eliminates all harmonics abovethe tenth from that portion of the operation cycle of the clawcomprising the filmadvancing portion-thereof,- whereby the accelerationcurve of that portion of the claw is devoid of sharp corners and suddenchanges in magnitude.

JASPER S. CHANDLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number 7 Name Date 1,978,878 Bundick Oct. 20; 19342,059,206 v Carson l s= s Nov. 3, 1936 2,461,159 Hutchison Feb. 8, 1949FOREIGN PATENTS Number Country Date 521,086 Germany Mar. 18, 1931v

